I can see Myths and stories as being important for inculcating values. I remember listening to Gita and Bible stories as a kid. I also liked learning the Greek, Roman, and Egyptian Mythology. Last time I was interested in mythology into I have been into Zen koans, Native-American tales, and tales of Anansi the Spider (not sure why, I was fascinated by his trickery).
For some reason, I wasn't thinking of Mythology as literature. But I suppose a lot modern literature (and even TV, pop-Novels) forms the common idioms that shape our discourse. But wouldn't we pick up those idioms through the discourse without reading a lot of literature?
Nonononono. When I used the word "mythology," I meant something bigger than just Ovid's
Metamorphoses, the stories about the Greek gods. I meant those too, but also Hemingway. Heck, as you rightly observe, even the hitmen in Pulp Fiction have (God help us) become part of the ongoing conversation. Like you, I wasn't really thinking of "mythology" as literature, though...I was thinking of literature as mythology.
As for picking up idioms through the discourse without reading a lot of literature, well, sure, you can do that...if you only want to acquire
this week's culture. If you really want to understand what Tarrantino was saying through John Travolta, however, you have to know Sam Peckinpah, and before him John Ford, and before him Zane Grey, and before him John Milton, and before him Moses.
Art (and literature is a kind of art) is contextual. The history of art is the context in which the current works are interpreted. I'm really just a beginner at such interpretation, but even I can see that it's so.